Complementarity in the use of nitrogen forms in a temperate broad-leaved mixed forest

Abstract

Background: The complementary use of different forms of soil nitrogen (N) might lead to a higher productivity of mixed forests than monocultures, but convincing evidence for temperate mixed forests is scarce.

Aims: We searched for species differences in N uptake rates and the preference for NH₄⁺, NO₃⁻ or glycine among five temperate broad−leaved tree species (Acer pseudoplatanus, Carpinus betulus, Fagus sylvatica, Fraxinus excelsior, Tilia cordata) in a mature mixed stand.

Methods: ¹⁵N tracer was added to the soil and its accumulation in fine root biomass was analysed after 10 min, 1 h and 1 d.

Results: The estimated root uptake rates of the species were in the range of 5–46 µg N g⁻¹ root h⁻¹ for NH₄⁺, 6–86 µg N g⁻¹ h⁻¹ for NO₃⁻ and 4–29 µg N g⁻¹ h⁻¹ for glycine during the first hour after tracer application. Carpinus, Tilia and Acer tended to prefer NH₄⁺ over NO₃⁻, while Fraxinus showed equal preference for both N forms and Fagus seemed to prefer NO₃⁻.

Conclusions: The five co-existing tree species differed in uptake rates and partly in their N form preference, but complementarity in the use of different N forms seems to be of minor importance in this forest because tree species appear to be rather flexible in their N form use.

Keywords:

• Acer pseudoplatanus
• ammonium
• Carpinus betulus
• Fagus sylvatica
• Fraxinus excelsior
• glycine
• nitrate
• root uptake
• Tilia cordata
• ¹⁵N tracer

Acknowledgments

This study was funded by the Deutsche Forschungsgemeinschaft (DFG, GRK 1086 ‘The role of biodiversity for biogeochemical cycles and biotic interactions in temperate deciduous forests’). We are grateful to the National Park administration for the permission to conduct the study in Hainich National Park.

Additional information

Notes on contributors

Andreas Jacob

Andreas Jacob has conducted his Ph.D. research at the University of Göttingen with a primary focus on below-ground processes in forest ecosystems and the role of tree diversity effects.

Christoph Leuschner

Dr. Christoph Leuschner is professor of plant ecology, with a research focus on the ecology of temperate and tropical forests.